The current oil lifting equipment available in oilfields, pumps out a three-phase mixture of gas, oil and water during its downhole operation. The gas in the mixture has a significant influence on the efficiency of the artificial lifting equipment. For example, when the submergence depth of the oil well pump is within a normal range (150˜500 m), the pump efficiency is only 30-40% on average. All kinds of previously developed downhole gas-liquid separation devices, i.e., gas anchors, function as follows; a large amount of mixture is first introduced into the gas anchor, and then undergoes the gas-liquid separation in a swirling flow through various flow passages in the gas anchor. This method suffers very low separation efficiency, especially for downhole fluid with a viscosity greater than 2 mPa·s, and thus can hardly realize an objective of improving pump efficiency and increasing oil production in field applications. As yet there is no method or device that enables effective oilfield downhole gas-liquid separation when a pumping unit swabs downhole fluid, especially for fluid with a viscosity greater than 2 mPa·s. In view of this problem, the inventor has disclosed an oil well downhole gas-liquid separation method and a multi-cup uniform flux gas anchor in Chinese Patent No. 200310117207.9 which employs a principle of extending the separation time of the produced fluid, where a plurality of settling cups are installed on a central pipe. Through multi-cup flow distribution, the single-cup fluid flow rate is significantly decreased, which ensures that the settling speed of the fluid in the settling cup is greatly decreased, thereby enabling the two-phase fluid of gas and liquid to be separated in the settling cups.
However, it is known from the Stokes' Law that the gas rising speed is proportional to the square of the diameter of gas bubbles. The settling cup used in the Patent 200310117207.9 has a smooth external surface, and extends in a streamlined profile, such that small gas bubbles are evenly distributed along the external side of the cup, and are less likely to contact each other, which does not facilitate aggregation of the small gas bubbles.